Generally, an image recorded on a paper for example, through subtractive color mixing has a narrower color reproduction range than a displayed image that is outputted through additive color mixing. With this fact, in the technical field adopting the subtractive color mixing for outputting an image as a result of image processing, there have been inquisitions for various color materials or researches of usage of fluorescent materials so as to enlarge color reproduction range and to improve hue.
One example of such researches for realizing enlargement of color reproduction range and improvement of hue can be found in a color image forming method disclosed in Japanese Laid-Open Patent Application Tokukai 2000-181170 (published on Jun. 30, 2000). According to this image forming method of the Document 1, colors are compensated during formation of a hard copy through subtractive color mixing by adding a fluorescent material to ink (color material) of a color component so as to enlarge color reproduction range and/or improve hue. With this method, the Document 1 obtains a color reproduction range almost as wide as that of an image outputted through a CRT (Cathode-Ray Tube) even for a hard copy reproduced based on the subtractive color mixing.
More specifically, the method of the Japanese Laid-Open Patent Application Tokukai 2000-181170 (hereinafter referred to as a Document 1) carries out additive color mixing with respect to ink of a coloring component used for a color image forming method, by adding a fluorescent material having a luminescence characteristic to the ink. This results in cancellation of sub-absorbency, which is a characteristic of the ink of a coloring component. Namely, the Document 1 realizes enlargement of color reproduction range by carrying out subtractive color mixing with ink of a color component which additionally includes a fluorescent material.
Further, as described in the foregoing publication Tokukai 2000-181170 in Paragraph 0011, the color compensation in the foregoing case refers to generation of change in at least one of absorbency of color, absorption waveform, half value breadth, absorption peak, color purity, brightness and saturation. Accordingly, the foregoing color compensation is performed by changing absorbency etc. of color in the ink of a color component.
Further, According to the Document 1, the fluorescent material is added to the ink of a color component in an amount or in a ratio for offering −0.3 or greater absorbency throughout the whole wavelength. Note that, in the embodiments described in the Document 1, the compounding ratio of the fluorescent material added to the ink of a color component is specified at or lower than 5%. The document 1 states that this ratio is determined in consideration of suppression of fluorescence generated in the ink of a color component, so as to get rid of other effects than color compensation.
However, image output induces no degradation of picture quality in some cases even with the fluorescence generated by addition of a fluorescent material into the ink of a color component, since the brightness of fluorescent ink is enhanced and results in superior picture quality. Further, there are some difficulties in practice to cancel the sub-absorption of the ink of a color component only by the addition of a fluorescent material in a ratio of as small as around 5% to the ink of a color component. Besides, the addition of this amount causes few changes in hue, brightness or saturation of the ink. As a result, neither color compensation nor enlargement of color reproduction range can be achieved.